California, Colorado and New Mexico have the highest risk of plague

Parts of central Colorado, north-central New Mexico and southwestern and northeastern California have the highest risk for human exposure to plague, new research suggests.

The scientists said their findings, which are based on cases of plague reported in both wild and domestic animals between 2000 and 2015, could help public health officials better monitor the infection, which can be deadly in humans.

In recent years, seven human plague cases have been reported, on average, each year, affecting people of all ages. Half of reported cases involved people between the ages of 12 and 45, according to the U.S. Centers for Disease Control and Prevention.

"The findings can be used by public health agencies to target specific areas for enhanced plague surveillance within areas and counties predicted to be at high risk, as well as by other research teams to direct the sampling of local wildlife populations for the identification of Yersinia pestis in wild animals that find themselves in close proximity to humans and human developed landscapes," said researcher Michael Walsh.

An assistant professor of epidemiology and biostatistics with the School of Public Health at SUNY Downstate in New York, his comments appeared in a university news release.

Plague was introduced into the United States in 1900, according to the CDC. Rat-infested steamships sailing from affected areas brought the disease, which is caused by Yersinia pestis bacteria found in rodents and their fleas.

The last urban plague epidemic in the United States occurred in Los Angeles in 1924 and 1925. After that outbreak, plague spread from urban rats to rural rodent species. This caused plague to become entrenched in many areas of the western United States.

Most human cases have been reported in rural areas of northern New Mexico, northern Arizona and southern Colorado; and in California, southern Oregon and far western Nevada, the researchers said. ■